Molluscs

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  • Molluscs
    • key features
      • bilateral symmetry
      • triploblastic
      • coelomates
      • protostomes
      • 93000 species
      • marine F.W terrestial
      • seafood
    • body plan
      • muscular foot
        • movement
      • visceral mass
        • contains internal organs
      • mantle
        • fold of tissue over visceral mass that secretes a shell
      • nervous system
        • nerve ring round oesophagus with ventral nerve cords
      • digestive system
        • radula and long digestive tract with coiled visceral mass
      • circulatory system
        • open circulatory system, dorsally heart pumps haemolymph through arteries into sinuses
      • excretory system
        • nephridia removing metabolic waste from haemolymph
    • classification
      • Gastropoda - marine FW snails torsion in shells
      • 8 classes but we only need 4
      • Bivalvia - marine flattened shell, (clams) filter feeder, attach to rocks by tentacles. parasitic youth
      • cephalopoda - marine squid, head with tentacles, siphon jet locomotion, carnivore, poison, spermatophores
      • Polyplacophora - marine chitons oval shell with 8 dorsal plates no head separate sexes ferilise externally settle as youth

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